Cracking of reduced crude with catalyst and inert particles



Nov. 1955 E. w. s. NICHOLSON 2,723,223

CRACKING OF REDUCED CRUDE WITH CATALYST AND INERT PARTICLES Filed May10, 1951 1A- Zo a I Q D QHEATEQ-----:F 3A

EAToQ r"if" '21 L iei is) II "10 [I A r. 10 u Edward Z0: 5. QihcLSon. Smcoco! Unite 2,723,223 Patented Nov. 8, 1955 lice CRACKING F REDUCEDCRUDE WITH CATA- LYST AND lZNERT PARTICLES Edward W. S. Nicholson, BatonRouge, La, assignor to Esso Research and Engineering Company, acorporation of Delaware Application May 10, 1951, Serial No. 225.55%

2 Claims. (Cl. 196-52) The present invention relates to a process oftreating hydrocarbons. More particularly, the invention pertams to amethod of producing from relatively heavy or highboiling hydrocarbonoils of the type of topped or reduced crude or similar heavy residuesincreased quantities of motor fuel range fractions of improved qualityas well as higher boiling distillate fractions suitable for furthercracking. Broadly, the invention involves the catalytic cracking ofheavy residues of the type mentioned above wherein the feed is contactedwith fluidized catalytically inert solids and cracking catalyst.

In conventional petroleum refining, the crude petroleum is firstdistilled to produce various distillate fractions and a residue boilingabove about 700 F. Motor fuels are normally produced from the distillatefractions by suitable refining processes including thermal or catalyticcracking, reforming, isomerization, alkylation, etc., while the residueis worked up to yield marketable high-molecular Weight products, such aslubricating oils, waxes, asphalt, fuel oils, etc. More recently,however, the demand for motor fuels has increased so greatly that it hasbecome desirable to use the residues from the crude distillationextensively as an additional source of raw materials for motor fuels.

It has been known for a long time that motor fuels may be produced bycoking crude residua, that is by subjecting the residues to cracking atsevere conditions including relatively high temperatures and longholding times. The use of cracking catalysts in this reaction haslikewise been proposed. However, serious difiiculties have beenencountered in this type of operation chiefly as the result of the highash content of the feed and the high rate of coke formation. Aside fromthe fact that the heavy coke deposits in the coking vessels and transferlines require frequent cleaning periods and plant shut-downs, catalystcontamination and deactivation by coke and difficultly removable ashconstituents of the feed is so rapid that crude residua have beenconsidered highly undesirable as feed stocks for conventional catalyticcracking processes.

Some of these difficulties may be avoided in accordance with priorsuggestions by coking residues in a dense turbulent bed of hotsubdivided catalytically inert solids, such as coke, pumice, kieselguhr,spent clay, or the like fluidized by upwardly flowing gases or vapors.These solids serve primarily as a carrier for the coke formed and as ascouring agent preventing coke deposition on equipment walls. Alsogasoline yields are somewhat higher as a result of the high surface areaof the solids. The coke deposited on the solids may be burnt oil in aseparate fluid-type heater vessel from which hot solids may be returnedto supply heat required for cooking. It is a matter of record that fluidoperation aifords greatest advantages with respect to heat transfer andeconomy, temperature control, ease and continuity of operation, etc.

While procedures of this type avoid catalyst contamination and heatsupply by circulating catalyst, they are essentially thermal rather thancatalytic in character and, therefore, result in the production of motorfuels of relatively low octane rating. The addition of a crackingcatalyst in itself to the inert material is no complete solution of theproblem because there still remains the difliculty of catalystcontamination and deactivation by ash constituents of the feed, whichcannot readily be removed by simple oxidativc regeneration. The presentinvention overcomes these diiiiculties.

It is, therefore, the principal object of the invention to provideimproved means for producing motor fuels by coking heavy residua incontact with fluidized inert solids and cracking catalysts. Otherobjects and advantages will appear from the description of the inventiongiven below wherein reference will be made to the accompanying drawing.

In accordance with the present invention, heavy residues of the typespecified above are coked by passing the feed at coking conditionsupwardly through a fluidized mass consisting of relatively coarse inertsolids and of relatively fine cracking catalyst in such a manner thatsubstantial upward elutriation of relatively fine catalyst fromrelatively coarse inert solids takes place with the elfect that the feedis maintained at cracking conditions in contact with a mixture of acatalytically inert mass of solids and cracking catalyst. Fresh activecracking catalyst of relatively small particle size is continuouslysupplied to this bed and removed therefrom by elutriation substantiallyat the same rate at which it is contaminated. In this manner, the solidsmixture is continuously maintained at a desirable level of catalyticactivity and selectivity to valuable volatile conversion products. Inaddition to being of smaller particles size, the catalyst may be oflower density to permit or enhance this type of operation. It has alsobeen observed that the relative entrainment rate of the smaller orlighter particles is substantially increased when coke is preferentiallydeposited thereon. This takes place in the case of the present inventionbecause of the higher cracking activity of the catalyst particles ascompared with that of the inert material.

The preferred embodiment of the invention provides for a single-passoperation with respect to the catalyst. The oil stream containing therelatively small sized and/ or low density catalyst may be preheated ina conventional coil furnace and then superheated to crackingtemperatures by addition of relatively coarse and/or dense inert solidscirculated from a burner vessel. The catalyst may also be addedsubsequent to the addition of inert solids. When the mixed feed entersthe reactor, catalytic cracking takes place in the fluidized state andthe more entrainable catalyst passes overhead with the product oilvapors and may be separated from the product oil in gas-solidsseparators, slurry settlers and/ or other conventional means, to bewithdrawn from the system. Elutriation of catalyst from the densefluidized phase may be enhanced by providing a perforated grid orpacking above the dense phase or raising the dense phase level so as toreduce the volume of the disperse phase within the reactor to a,minimum. The less entrainable inert solids may be downwardly withdrawnfrom the dense phase and circulated to a burning vessel to be reheatedtherein and to be returned to the reactor for heat supply. Thisoperation eliminates the recycle of catalyst contaminated with feedcontaminants which would cause poor product distribution. The catalystcontaining such contaminants is continuously discarded, preferably afterpassage through the burner vessel, and essentially all the crackingtakes place in contact with fresh relatively uncontaminated catalyst.

Fluidization conditions may be maintained within conventional ranges.The relative particle sizes of the catalyst and inert solids depend, ofcourse, to a certain extent on their relative densities. Assumingsubstantially equal densities of the order of that of coke andconventional natural or synthetic clay catalysts, the inert solids mayhave a particle size of about 100500 microns and the catalyst a particlesize of about 80 microns and less. Linear superficial velocities of thefluidizing medium in the cracking zone may vary from about 0.5-10 ft.per sec. to establish apparent densities in the dense mixed solids phaseof about 10-50 lbs. per cu. ft. and about 0.001-1 lb. per cu. ft. in thedisperse phase.

Reaction conditions may include oil preheating temperatures of about300900 F., coking and cracking temperatures of about 8001200 R, andinert solidsregeneration temperatures of about l050l500 F. or higher. Inthe cracking operation, the ratio of total solids to oil may be fromabout 1:1 to about 20:1 by weight. The proportion of inert material tocatalyst may be from about :1 to about 1000:1 by weight.

While some of the inert solids previously suggested for the coking ofresidues in fluid operation such as sand, pumice, spent clays, silicagel, etc. may be used, coke affords greatest advantages in the processof the invention because product coke deposited on this material forms avaluable by-product which may be recovered as a high B. t. u. fuel, as araw material for activated carbon, and for other purposes. Extraneouscoke from petroleum or coal may be used to start up the process whilethereafter product coke may serve as the inert solid. The product cokemay be Withdrawn and at least part of it ground to provide fresh seedcoke. An alternative method for continuously providing seed coke withoutWithdrawing product coke from the unit is the inclusion of a supersonicattriter in the coke cycle as it is known in the art of fluid catalyticcracking. While conventional cracking catalyst including activatedclays, activated alumina, synthetic composites of silica with alumina,magnesia and/ or boria, etc., may be used, inexpensive expendablecatalysts of moderate activity such as activated carbon, Attapulgusclay, etc. are preferred.

Having set forth its objects and general nature, the invention will bebest understood from the more specific description hereinafter read withreference to the drawing, the single figure of which is asemi-diagrammatical illustration of a system suitable to carry out apreferred embodiment of the invention.

Referring now in detail to the drawing, a crude residuum such as an 8%bottoms fraction from the vacuum distillation. of a West Texas crude ora similar heavy residue maybe admixed in line 3 with about 550 lbs./bbl.of an expendable catalyst such as activated carbon or Attapulgusclaysupplied through line 5. The catalyst may have a particle size. ofup to about 80 microns. The catalyst-oil mixture may be preheated. in aconventional coil furnace indicatedat 7, to temperatures of about 600900F. The preheated feed may then be admixed in line 8 with hot inert.solids having a particle size of about 100-500 micronssupplied from aconventional standpipe 9 provided with aeration and/or stripping taps t,the solids being at a temperature of about 10001500 F. and in amounts ofabout 7003,000 lbs./bbl. The mixture in line 8 may have a temperature ofabout 8001200 F. conducive to cracking and complete vaporization of theoil. The solidsin-gas suspension formed may enter reactor 10 through adistributing grid 12. Feed rates and reactor design are so chosen that adense, turbulent, fluidized mass of solids Mm having an interface Linand an apparent density of about -50 lbs. per cu. ft. is formed whichprovidesfor an additional vapor contact time of about 210 seconds,catalyst being selectively entrained in. the product vapors and carriedoverhead to. form a disperse phase D10 having an apparent density ofabout 0.0020.1 lbs. per cu. ft. in which crackingiscompletedi. .Linearsuperficialvapor velocities in reactor. 10 of about 2l0 ft. per see. arenormally suitable-for these purposes. This entrained catalyst will carrythe bulk of the coke produced by'cracking in vessel 10 becauseit iscontinuously supplied in a fresh highly active state. Product vapors andentrained catalyst are withdrawn through cyclone 14 and thence throughline 16 to conventional product recovery equipment, if desired afterfurther separation of entrained catalyst in any suitable manner knownper se. Catalyst separated in cyclone 14 may either be returned via line18 to mass M10 for control of hold up and/or apparent density ordiscarded through line 20, and/ or passed through line 21 to reheater 26to generate heat therein as will appear hereinafter.

Fluidized solids consisting predominantly of coarse inerts concentratingin the lower portion of reactor 10 and containing by far the largestproportion of the non-catalytic coke, i. e. the coke formed from thenon-vaporizable asphaltene constituents of the feed by vaporization andthermal cracking may be withdrawn through conventional standpipe 22 andsupplied to line 24 substantially at the rate of solids flow throughline 9. The inert solids are picked up in line 24 by air and carried indilute suspension to a lower portion of reheater 26 through adistributing grid 28. The air feed rate to reheater 26 may be socontrolled that the inert solids are reheated therein by combustion ofcoke to about l0001500 F. in dense phase fluid operation at superficiallinear gas velocities of about l-1O ft. per sec. Flue gases containingentrained solids may be withdrawn through separator 30 and line 32,separated solids being returned through line 34 or discarded Via line36. Make-up inert solids may be supplied through line 38. Hot inertsolids may be supplied via standpipe 9 to line 8 as described above. ifthe carbon deposited on the inert solids in reactor ill is insufficientto maintain by combustion the desired temperature in reheater 26, atorch oil or fuel gas may be injected to the reheater through line 40.Preferably, additional heat is generated by supply of coked catalystthrough line 21 as described above. Catalyst particles subjected tocombustion in reheater 26 may be removed therefrom by entrainment in theflue gases and discarded.

If desired, a horizontal grid plate similar to plate 12 but having ahigher percentage of open area may be arranged in the upper portion ofreactor 10 to promote the formation of a second fluidized bed in reactor10 above bed M10 on top of the second grid plate, thus to enhance theutilization of the catalyst before it is disprises feeding carded.Rather than supplying the fresh catalyst mixed with the oil feed to line3, the fresh catalyst may be added through line 42. after the additionof the inert solids.

Catalyst removal from the system by entrainment from mass M10 has beenabove referred to. It should be understood, however, that catalystremoval may also bev accomplished by passing substantially all thecatalyst contained in mass M10 together with inert solids through lines22 and 24 to reheater 26 from which the catalyst may; be removed byentrainment substantially as described above. For this purpose, it issufficient to run reactor it] at relatively low fluidizing velocitiesof, say, 0i5-3 ft. per sec. and reheater 26 at relatively highvelocities conducive to catalyst elutriation.

While in the above examples reference has been made to the use ofcatalyst in a form more readily entrainable than the inert solids andthis is the preferred embodiment of the invention, it is noted that someof the advantages of the invention may be secured when the inert solidsare used in a more readily entrainable. form than the catalyst. Ifdesired, the systems illustrated may be readily adapted to this type ofoperation in a manner obvious to those skilled in the art.

The foregoing description and exemplary operations have served toillustrate specific embodiments of the invention but are not intended tobe limiting in scope.

What is claimed is:

l. The process of converting heavy residual hydrocarbon oil to morevolatile products and coke, which comsaid oil in preheatedcondition-into contact with (a) a small proportion, between about 5 and50 pounds per barrel of feed, of finely divided preheated expendablesolid catalyst and (b) at least 5 times as large a proportion, comparedto the weight of catalyst, of relatively coarse, preheated,catalytically inert solid particles from which the finely dividedcatalyst can be readily elutriated, passing a gasiform fluid upwardlythrough a mass of said. catalyst and inert solids in a contacting zoneso as to maintain said mass in fluidized condition and at such velocityas to substantially completely elutriate the catalyst therefrom after acontact time of about 2 to 10 seconds between oil and catalyst in thecontacting zone, and thereafter withdrawing, reheating and recycling tothe reaction zone at least a portion of the inert solids, substantiallyfree of catalyst to maintain a cracking and coking temperature between800 and 1200 F. in said zone.

2. Process according to claim 1 wherein 700 to 3000 pounds of inertsolids are fed into the reaction zone for each barrel of feed.

References Cited in the file of this patent UNITED STATES PATENTS2,166,544 Cross July 18, 1939 2,382,755 Tyson Aug. 14, 1945 2,446,247Scheineman Aug. 3, 1948 2,543,884 Weikart Mar. 6, 1951 2,573,906 HuffNov. 6, 1951 FOREIGN PATENTS 118,399 Australia Apr. 12. 1944

1. THE PROCESS OF CONVERTING HEAVY RESIDUAL HYDROCARBON OIL TO MOREVOLATILE PRODUCTS AND COKE, WHICH COMPRISES FEEDING SAID OIL INPREHEATED CONDITION INTO CONTRACT WITH (A) A SMALL PROPORTION, BETWEENABOUT 5 TIMES AS 50 POUNDS PER BARREL OF FEED, OF FINELY DIVIDEDPREPHATE EXPENDABLE SOLID CATALYST AND (B) AT LEAST 5 TIMES AS LARGE APROPORTION, COMPARED TO THE WEIGHT OF CATALYST, OF RELATIVELY COARSE,PREHEATED, CATALYTICALLY INERT SOLID PARTICLES FROM WHICH THE FINELYDIVIDED CATALYST CAN BE READILY ELUTRIATED, PASSING A GASIFORM FLUIDUPWARDLY THROUGH A MASS OF SAID SATALYST AND INERT SOLIDS IN ACONTRACTING ZONE SO AS TO MAINTAIN SAOD MASS IN FLUIDIZED CONDITION ANDAT SUCH VELOCITY AS TO SUBSTANTIALLY COMPLETELY ELUTRATE THE CATALYSTTHEREAFTER A CONTACTING, RETIME OF ABOUT 2 TO 10 SECONDS BETWEEN OIL ANDCATALYST IN THE CONTACTING ZONE, AND THEREAFTER WIDTHDRAWING, REHEATINGAND RECYCLING TO THE REACTION ZONE AT LEAST A PORTION OF THE INERTSOLIDS, SUBSTANTIALLY FREE OF CATALYST TO MAINTAIN A CRACKING AND COKINGTEMPERATURE BETWEEN 800 AND 1200* F. IN SAID ZONE.